Systematic study on Gondwanan plant, Podocarpus (Podocarpaceae)

Podocarpaceae科有17属，约125种（Page, 1990），主要分布于南半球。podocarpacae科的生态习性是多样化的，其下科分类包括科的划分一直存在问题。本研究旨在建立编码atpB、matK和rbcL基因的叶绿体序列数据库，以重建该科的分子系统发育，并利用该系统发育来解决Podocarpus属的划分问题，即Podocarpus sensu stricto、Afrocarpus、Nageia、Decussocarpus、Retrophyllum、Parasitaxus、Prumnopytis和Sundacarpus属之间的系统发育关系。Podocarpus属与Afrocarpus属、Nageia属、Decussocarpus属和Retrophyllum属是单系的，而Parasitaxus、Prumnopytis和Sundacarpus属与该属无关。后者位于该科的基部分支，与lagarostrobs属、lepidothamus属、Phyllodadus属和Halocarpus属构成一个单系类群。de Laubenfels（1969, 1985）提出的Podocarpus属的近属分类得到了分子系统发育学的有力支持。气孔上是否存在Florin环和叶片形态等形态特征是系统发育的信息特征。本研究结果表明，早在白垩纪（冈瓦纳大陆分裂之前），Podocarpus的物种就已经进化为两个亚属，并且每个亚属的物种在南半球的每个地区都是独立进化的。

The family Podocarpaceae is composed with 17 genera and ca. 125 species (Page, 1990), and is mainly distributed in the southern hemisphere. The family Podocarpaceae is diversified in their ecological habit, and its infrafamilial classification including the circumscription of the family has been problematic. This study aims to construct a sequence database for the chloroplast encoded atpB, matK and rbcL genes in order to reconstruct a molecular phylogeny for the family and to use this phylogeny to address the circumscription of the genus Podocarpus, I.e., phylogenetic relationships among the genera of Podocarpus sensu stricto, Afrocarpus, Nageia, Decussocarpus, Retrophyllum, Parasitaxus, Prumnopytis and Sundacarpus. The genus Podocarpus is monophyletic with genera of Afrocarpus, Nageia, Decussocarpus and Retrophyllum, however, Parasitaxus, Prumnopytis and Sundacarpus are unrelated to the genus. The latter group is located on the basal clade within the family and makes a monophyletic group with genera of Lagarostrobos, Lepidothamnus, Phyllodadus, and Halocarpus. Infrageneric classification of the genus Podocarpus suggested by de Laubenfels (1969, 1985) was strongly supported by the molecular phylogeny. Morphological characteristics such as presence or absence of Florin ring on stomata and morphology of leaves were revealed to be informative characteristics for the phylogeny. The present result indicates that species of Podocarpus had already evolved into the two subgenera until Cretaceous (prior to breakup of Gondwanaland), and species of each subgenus was independently evolved in each area of the southern hemisphere.